SOME USEFUL PLAXTS 339 



latter. These "nitrogen-fixing bacteria" therefore afford 

 an unlimited supply of nitrogen available for the nutrition 

 of the higher plants almost without expense to the farmer 

 and gardener. 



(5) TANXIXG MATERIALS, DYES, VARNISHES, AND 



MISCELLAXEOUS PRODUCTS OF 



VEGETABLE ORIGIN 



414. Many of the substances mentioned under this head 

 are fully discussed in treatises on the chemistry of various 

 manufacturing industries. All that can be done in this 

 place is to give a few examples of plant products used in 

 manufacturing processes. 



^^egetable dyes are no longer nearly as important as 

 they were before the discovery of aniline colors. Antique 

 Oriental rugs and other articles, however, show well how 

 much superior are the soft shades produced by dyes of 

 vegetable origin. A large number of dyestuffs are ob- 

 tained from tropical or sub-tropical plants of the Pea 

 family ; among these are Brazil wood, logwood, camwood, 

 and indigo. 



Varnishes usually consist of some kind of rosin dis- 

 solved in alcohol, oil of turpentine, or linseed oil. Among 

 the most valuable varnishes are shellac (from trees of the 

 Mulberry family), copal (Pea family), and Japanese lacquer 

 (Sumach family). 



Common rosin and turpentine are made from the sap of 

 pine trees, particularly our longleaf southern pine. Deep 

 cuts are made through the bark into the wood, and from 

 these a pitchy liquid slowly flows. By distilling, this 

 is separated into a nearly colorless liquid, oil of turpentine, 

 commonly called " spirits " of turpentine, and the familiar 



